Essington et al.: Shifts in the estuarine demersal fish community after a fishery closure in Puget Sound, Washington 
211 
Table 2 
Comparison of 3 models of changes in catch rates of species or species groups commonly collected 
during bottom trawl surveys conducted from 1991 to at Port Madison, Puget Sound, Washington. 
Akaike’s information criteria adjusted for small sample size (AIC c ) was used to choose between the 
models compared: constant (no change), linear (change through time), or change point (abrupt change 
at a single point in time, with no temporal change elsewhere). Values indicate a difference in AIC c for 
each species from lowest AIC c among all species. No result is given for species for which the change- 
point model estimated a breakpoint in the first 4 or last 4 years of the time series and, therefore, 
these species could not be considered in change-point model comparisons. 
Species 
Constant 
AAIC c 
Linear 
Change point 
Blackbelly Eelpout ( Lycodes pacificus) 
1.98 
0.00 
- 
Dover Sole (Microstomus pacificus ) 
31.07 
12.95 
0.00 
English Sole (. Parophrys vetulus) 
65.77 
26.91 
0.00 
Flathead Sole ( Hippoglossoides elassodon) 
28.70 
0.00 
- 
Pacific Hake ( Merluccius productus) 
21.37 
16.74 
0.00 
Pacific Herring ( Clupea pallasii ) 
9.62 
0.00 
- 
Pacific Tomcod iMicrogadus proximus ) 
30.74 
19.15 
0.00 
Plainfin Midshipman ( Porichthys notatus) 
19.94 
0.00 
- 
Rock soles ( Lepidopsetta bilineata and L. polyxystra) 
154.96 
82.95 
0.00 
Sanddabs ( Citharichthys sordidus and C. stigmaeus ) 
30.06 
18.88 
0.00 
Sand Sole (Psettichthys melanostictus) 
28.72 
23.23 
0.00 
Shiner Perch ( Cymatogaster aggregata) 
15.22 
11.95 
0.00 
Slender Sole ( Lyopsetta exilis) 
82.67 
38.21 
0.00 
Spotted Ratfish (. Hydrolagus colliei) 
0.00 
0.23 
- 
Discussion 
We hypothesized that the data from Port Madison 
would reveal trends of increasing abundance in resi- 
dent groundfish populations in Puget Sound after the 
cessation of commercial bottom trawling and, thereby, 
would indicate rates and magnitudes of recovery. Be- 
fore the ban on commercial trawling in the central ba- 
sin of Puget Sound, commercial catches ranged from 
224 metric tons (t)/year to more than 500 t/year and, 
therefore, likely represented a significant source of 
mortality for many targeted species. 6 Commercial fish 
catches through other methods (set nets, purse seines, 
or set lines) also have been reduced sharply. 5 However, 
most species exhibited nonlinear patterns of abun- 
dance characterized by abrupt and sustained changes 
in relative abundance indices during the 21-year time 
period that the survey spanned. These abrupt abun- 
dance shifts were notable because they were most com- 
monly in the opposite direction from our expectation 
and appeared to be synchronous among different com- 
mon groundfish species. Moreover, these shifts did not 
appear to be related to demographic changes indicative 
of recruitment shifts, and they were not linked to tem- 
poral patterns in local water temperature and salinity. 
6 Schmitt, C. S., S. Quinnell, M. Rickey, and M. Stanley. 1991. 
Groundfish statistics from commercial fisheries in Puget 
Sound, 1970-1988. Progress Report No. 285, 315 p. Wash- 
ington Department of Fisheries, Olympia, WA. 
Currently, no recruitment time series are available for 
demersal fishes in Puget Sound. 
There are several possible explanations for the syn- 
chronous reduction in catch rates of groundfish species 
that occurred in the late 1990s to early 2000s. The first 
is loss or impairment of habitat that resulted in emi- 
gration out of the survey area. Most of these groundfish 
species reside on soft-bottom habitats (sand or mud) 
and do not rely on biogenic habitats, such as eelgrass 
beds, that are particularly vulnerable. However, Nich- 
ols (2003) reported an increase in abundance of com- 
mon prey items of English Sole in Port Madison and in 
nearby areas from the early 1960s to the early 1990s. 
It is possible that this trend reversed after this time 
period, although direct data are needed to evaluate 
this hypothesis. Alternatively, trawling itself may have 
altered physical habitat and benthic infaunal commu- 
nities (Auster et al., 1996); cessation of this activity 
may have promoted a community of less-preferred prey 
for these fish predators. Little information, however, is 
available on bottom habitat or infaunal community dy- 
namics to test any of these hypotheses. 
Alternatively, the second explanation is that changes 
in catch rates in Port Madison may reflect expansions 
and contraction of population ranges, possibly as a con- 
sequence of changes in population densities (MacCall, 
1990). However, the sharp decreases in abundance that 
we witnessed suggest a decline in densities throughout 
Puget Sound and a contraction to other habitats. This 
implication is not supported by data from bottom trawl 
